This invention relates to a method and apparatus for optically inspecting the peripheral surfaces of cylindrical article(s). The articles may be discrete parts or continuous, such as cables or tubing.
Many approaches have been made in an effort to inspect three-dimensional parts. Such inspection, to be thorough, is relatively difficult and expensive to perform. One of the major problems encountered in such inspection is that the parts and the inspection sensor must somehow be indexed, rotated or otherwise moved in relation to one another in order to accomplish 100% inspection of the surface. This becomes increasingly difficult by conventional means as the speed of the inspection process is increased.
Among the various inspection systems that have been employed to inspect cylindrical articles have been those which optically illuminate the entire peripheral surface for visual inspection. See, for example, U.S. Pat. No. 2,607,267. Others effect such complete illumination but rely on photoresponsive materials instead of the human eye to elicit an output signal. Visual inspection is inadequate for obvious reasons--it is too slow and is subject to human judgmental error. The other approaches generally are not specific.
Following these early efforts, people have more recently used light beams such as laser beams to scan the surface of the cylindrical articles. To effect a complete inspection of the entire surface, the article is rotated about its longitudinal axis while the object is translated or the beam is traversed in a direction parallel to the axis.
In one system, disclosed in U.S. Pat. No. 3,834,822, for example, a cylindrical object to be inspected for surface defects is rotated about its axis and a collimated laser beam is axially scanned across the object's surface in a plane normal to the surface. The detectors, while symmetrically arranged on each side of the scanning plane, are of conventional design and detect light diffusely reflected in a limited angular range. Moreover, since there is no axial movement of the object being inspected, the inspection rate is significantly slowed and fewer articles can be inspected in a given time interval.
In regard to scanning techniques employed for moving objects, the major problem encountered has been the inability to detect reflected light with adequate responsivity to obtain a generally error-free, meaningful signal. A particular problem arises in inspecting cylindrical shells, such as shotgun shells, where it is necessary not only to detect surface flaws, but also anomalies in their geometrical configurations. The problem encountered here is the high speed with which the shells are passed through the inspection apparatus.